On-chip inductors are integral, passive circuit components that convert electrical current into magnetic energy for use in a variety of analog filter and voltage regulator circuits. More specifically, inductors convert any change in current into magnetic flux that, in turn, induces a voltage across the inductor. Inductors thus offer an ability to resist sudden changes in current and are widely used in applications as diverse as power substations to filters for radio frequency (RF) circuits and DC-DC power converters.
Because of the demands of planar fabrication processes, on-chip inductors may be spiraled metallic wire traces, typically copper, on the surface of a semi-conductor substrate that link the magnetic flux generated by the concentric coils to concentrate magnetic energy. Although the spiral geometry maximizes flux linkage for a two-dimensional system, limitations in fabricating highly-conducting, closely-spaced spiraled traces results in the consumption of a large chip area to create inductors of significant inductance. The complicated geometries of inductors have inhibited their ability to scale with other components of the on-chip circuits, and thus have become the limiting component in the down-scaling of some RF integrated circuits.